![]() ![]() In the above eample from site we see that memset was explicitly called but in our code, it was simply implied after setting up the construct and variable: "char command = "calc.exe" " like so. Fill 8 characters starting from str with '.' Since this is an imperfect de-compile of the C code, we reference the library methods to see how the actual structure of the source might look like (if we didn't already have the source code): // C program to demonstrate working of memset()Ĭhar str = "GeeksForGeeks is for programming geeks." We see the data 'calc.exe' being pushed onto the stack frame and set in memory by ' memset()' followed by our famous ' system()' call. What you see above is the subroutines in the main function. From the main view, find the left panel under functions/symbols and discover the 'entry' point as often you won't see the main() function properly parsed. When you first load the binary into Ghidra, you'll want to use the default 'automatic analysis' settings (select YES) before you get to the main screen. In this section, we're going to import the binary into Ghidra and start exploring the varying structure of the our original C shell code so we can identify the main() function, when variables are loaded, and the system() execution and compare it to our source code. For example, if you managed to isolate a sweet piece of malware that did not get detected and you want to mimic its TTP's. Let's analyze the binary in Ghidra so you can get a feel for what the code decompile looks like when you DON'T have the source code. Copy and paste the snippet below if you are running into this issue: _CRT_SECURE_NO_WARNINGSĬongratulations, you've compiled your first Win32 C-source shell code. Edit the macros and add in (case sensitive) the warning bypass macros to the definitions field. To do so, right click on your C file in solution explorer and set the configuration properties under 'preprocessor'. Windows defender at the time of this writing on Windows 10 does not flag the compiled binary. Note : This payload is detected as 'malware' from Chrome and Google Drive services. It's quite obvious what happens in the above snippet. It's not a full shell, but it's a starter template that uses native standard libraries so you can execute an external system call that will honor the Windows System32 directory path. In the above you see one of the simplest 'cmd only' forms of shell payload. System(command) //executes the calc.exe native path file So let’s get our first C-code template ready to go down below: #include //to use system() ![]() If we’re compromising and pivoting between Windows systems, we need to step it up. So why not write our own? Many tutorials you see focus on compiling or writing payloads for Linux. But these solutions, like any pre-made template aren’t always perfect and many vanilla payloads produced are caught by endpoint security solutions. So when we do pen testing engagements are go-to tool for shell payloads almost always includes Metasploit and specifically running either MSFVenom, Veil, and or some other C2 frameworks (in a post Empire world) that generates the desired shell code for you. Many cyber security professionals (including myself) aren’t experts in shell code creation nor the ancient C language. ![]() Writing your first Win32 Compatible Shell Payload in C Right click and ‘run as’ Administrator from the cmd terminal and then specify the installer msi to run so it does not fail. Optional: Metasploit Framework *Note: If you need to install this, there is an issue with the MSI installer.Ghidra from the NSA (ensure you install Oracle’s JDK 圆4 kit before you run the batch file).Visual Studio 2019 Community with the C++ Desktop Extensions and Packages.Payload binaries and source examined: systemcall_shellcode.c and reverse_winsocktcp_shellcode.c.All code or compiled binaries are provided ‘as is’ with no expressed warranty.įeel free to download and install these tools and follow along in the article to practice your win32-ninja shell code skills with us. The author takes no responsibility for any unauthorized activities performed using the information in this article. ![]() Are you ready? Let’s dive right in!ĭisclaimer: The methods, code examples, and techniques mentioned throughout this article for educational purposes only. We’ll examine samples using native windows libraries, compilers, C based shell payload, and Metasploit (MSFvenom) payload for Windows. The practical applications of malware analysis and reverse engineering efforts can help penetration testers improve their evasion techniques and achieve command execution on systems without Linux (or ported) tools against Windows systems. In this article, we’ll go over some example C code that is Windows x86 compatible and analyze binaries using Ghidra to help you write or improve upon your shell code skills by creating the payload first. Please note: All future articles will be on Medium. ![]()
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